The present invention relates to a method for assembling a rotary valve for hydraulic power assisted steering systems, especially for motor vehicles. The rotary valve includes a first valve element in the form of a rotary slide and a second valve element in the form of a control bushing, which can be rotated relative to one another. The control bushing and the rotary slide have longitudinal control grooves that interact with one another to direct a pressure medium from a source of pressure medium to a servomotor. Interacting control edges of the longitudinal control grooves of the control bushing and the rotary slide are formed parallel to one another. The control edges at least of the longitudinal control grooves of the rotary slide, which are connected to the source of pressure medium, and the control edges of the control bushing, which interact with the same, are formed so that they converge in an oblique manner at the same angle in relation to the longitudinal axis of the rotary valve.
A conventional method for assembling a rotary valve for hydraulic power assisted steering systems includes the following steps:
the rotary slide is inserted into the control bushing, which is connected firmly in terms of rotation to a valve output member, and displaced inwardly to a point just ahead of a stop in the region of the valve output member,
the two valve elements of the rotary valve are aligned in their central position with the aid of a pressure medium and are clamped in this position in a manner secure against rotation in relation to a torsion bar spring,
in order to determine the profile of a characteristic curve, the rotary valve is deflected fully in both directions and the pressure/angle or the pressure/torque ratio is recorded.
A method of this kind is used in assembling a rotary valve as described in European Published Patent Application No. 0 440 665, for example. The intention with this rotary valve is to reduce the width of the tolerance zone of the valve characteristic curves to a minimum.
It is an object of the present invention to provide an improved method for assembling a rotary valve so that different valve characteristic curves may be produced exactly with the same rotary valve components.
The above and other beneficial objects of the present invention are achieved by providing a method as described herein. This method allows the steering and handling of a vehicle to be modified without the need for different valve components. The solution is achieved by virtue of the fact that the basic characteristic curve determined is compared with a desired nominal characteristic curve from a predetermined family of nominal characteristic curves stored in software in an assembly device. The axial position of the rotary slide is adjusted until the desired nominal characteristic curve of the rotary valve has been achieved at least at a predetermined point. The rotary slide is then connected definitively to the torsion bar spring in a manner secure against relative rotation.
The different profiles of the valve characteristic curves represent approximately a parallel family of curves within the desired range. It is therefore necessary to select a point on the characteristic curve that is significant for the steering and handling of each type of vehicle. For this purpose, the desired servo pressure (or, alternatively, for the adjustment process, the valve deflection angle associated with this pressure) and the matching steering torque are determined for this point by driving tests.
A device provided for adjusting the valve characteristic in the steering valve should be capable of selecting any point (defined by the servo pressure and the associated steering torque) on the characteristic curve that has been determined in the driving tests and of permanently fixing the valve components, the rotary slide and the control bushing, relative to one another at this point (e.g., by drilling and pinning relative to one another).
To achieve this, it is necessary to control the characteristic-adjusting process by coordinate data (pressure/torque) using programmable software in order to produce a multiplicity of different characteristic curves that can be produced with pinpoint accuracy, i.e., without tolerances, in the most important range for assessment of handling, with identical standard valve components.
By virtue of this concept, it is possible to produce valve-characteristic profiles within a range of any desired size, even if the number of different valve components is reduced. This means a significant cost saving. An additional advantage is that this principle may be employed in the case of certain component features to make manufacturing processes that were previously expensive owing to close tolerances less sophisticated without having to accept wider tolerances in the characteristic curves.
Such a possibility is particularly advantageous in the case of passenger cars based on the common platform concept. It is possible to provide the different vehicles mounted on such a platform with steering characteristic curves that are xe2x80x9ctailor-madexe2x80x9d for them. This is possible with absolutely identical valve components stemming from a single basic steering system for this platform.